Stabilization of bleach baths



Patented Aug. 24, 1937 STABILIZATION F BLEACH BATHS poration of Delaware No Drawing. Application January 11, 1935, Serial No. 1,383

3 Claims.

This application relates to a process of increasing the stability of active oxygen yielding baths used in bleaching. More particularly, it relates to a process of treating acid wool bleaching baths such as are employed in the continuous bleaching of wool, so that the stability of these baths may be improved.

Ordinarily, the bleaching baths used in the bleaching of wool are dilute solutions of hydrogen peroxide which are acid in reaction. Ordinarily, the wool is bleached continuously in the bath and the active oxygen which is used up by the bleaching operation is replenished by the addition of more hydrogen peroxide solution to the bath as needed. For the bleaching of wool it is essential that the hydrogen peroxide concentration be within 1 and 3 volumes, and this is maintained by adding the required amount of a more concentrated solution of hydrogen peroxide.

The concentration of a solution of hydrogen peroxide is frequently expressed by stating the volume of the solution. Thus, it is customary to speak of a 1 vol. solution, a 2 vol. solution, a 50 vol. solution, a 100 vol. solution, etc. The volume of a hydrogen peroxide solution is expressed as the number of volumes of oxygen gas evolved from a volume of that solution when the gas is measured at 0 C. and a pressure of 760 millimeters of mercury. Thus, a 1 vol. solution at 20 C. yields 1 volume of oxygen gas per volume of solution under the standard conditions of temperature and pressure. Similarly, a 3 vol. solution yields 3 volumes of oxygen per volume of solution. The commercial solution of hydrogen peroxide sold for bleaching is generally a 100 vol. solution, or a solution of hydrogen peroxide yielding 100 volumes of oxygen gas per volume of solution. A solution of hydrogen peroxide of 100 volumes has a concentration by weight of hydrogen peroxide therein equivalent to approximately 27.6%. The commercial 100 vol. bleach solution is ordinarily diluted to the desired volume when it is introduced into the acid hydrogen peroxide bleach bath which constitutes the bath normally employed for the continuous leaching of wool.

Experience has indicated that acid wool bleaching baths decompose very rapidly. As such solutions are used continuously in daily plant operations, decomposition of solutions during use is to be expected, but it has also been discovered that decomposition occurs in such solutions in substantial amount even during those periods when the bath is not used in bleaching operations. Thus, even when the bleachery is shut down, such as over night, or over a week-end or a holiday period, it has been found that substantial and important losses in the active oxygen content of the bath occurs during the time that it is standing unused. Obviously, decomposition of the baths during standing, when no wool is being treated therein, is objectionable, wasteful, and increases the cost of operation. One of the purposes of this invention is to decrease the active oxygen loss by decomposition by increasing the stability of acid hydrogen peroxide bleaching baths, especially their stability during periods during which the baths are not in use.

It is accordingly one of the objects of this invention to devise a method by which active oxygen yielding baths, acid in reaction, such as those used in the continuous bleaching of wool, may be stabilized to prevent too rapid decomposition.

Another of the objects of this invention is to determine the causes for rapid decomposition, especially during those periods during which the bath is standing unused; and having discovered the causes, to remedy the conditions causing the ployed in continuous wool bleaching, may be 5 stabilized by treatment with an adsorbent cellulosic material. Briefly, the solution, or a portion of the solution, is filtered thru the cellulosic adsorbent. However, filtration is not essential, and any other method capable of insuring intimate contact between the cellulosic adsorbent and the solution may be utilized. In practice, the entire solution employed in wool bleaching may be filtered thru the adsorbent cellulose at such a rate that all the solution goes thru the adsorbent about once in every one to three hours. In practice, it will also be found convenient to by-pass a portion of the solution thru a cellulosic adsorbent and then return it to the bleach bath, such operations being carried out continuously, so that the bath is being continuously filtered.

We have found that catalytic impurities for example, metals such as iron, copper, nickel etc. 5 present in acid hydrogen peroxide bleaching solutions of l to 3 volume concentration are a primary cause of the decomposition of such solutions. Accordingly, it was with the purpose of eliminating to as large a degree as possible these catalytic metallic impurities that the treatment with an adsorbent cellulosic substance was devised. As previously indicated, though not essential, filtration thru the adsorbent cellulose is perhaps the simplest and most direct way for 5 insuring intimate contact between the two, so that the catalytic impurities may be adsorbed and removed by the cellulose.

In practice, in the continuous bleaching of wool, large vats are used 'to handle the dilute hydrogen peroxide solution. These vats, usually termed bowls in the trade, contain about 1,000 gallons of the solution, and :are in substantially continuous operation except during those periods in which the plant is shut down. For this reason it has been found most convenient to draw ofi" a portion of the bleaching liquid continuously thru a by-pass, allow it to filter thru the adsorbent cellulosic material, and then return it to the bowl. By this procedure the entire solution is eventually filtered, and a rate of filtration should be maintained such that the entire 1,000 gallons are permitted to flow thru the filter once in every one to three hours.

It is also within the scope of our invention to permit any portion of the bleaching liquid to fiow thru the cellulosic adsorbent in any given period of time as will enhance the stability of said liquid to any definite, desired degree. Thus, in practice, a certain amount of decomposition 40 due to impurities in the solution may not be objectionable, and it may be more expensive to circulate the entire contents of the bath thru the filter than to offset oxygen losses by the introduction of an additional amount of hydrogen peroxide solution. Under these conditions, it

may be more advantageous to treat only a portion of the hydrogen peroxide bleaching solution with the cellulosic adsorbent, either continuously or intermittently, thereby increasing the stability of the solution to-that degree which permits most economical operation. a In practice, we have foundthat the best results are obtained in the removal of the catalytic impurities favoring decomposition of hydrogen peroxide by the action of a cellulosic adsorbent if the pH of the solution is maintained Within the acid range, and more particularl within the limits 3.0 to 5.0. For most bleaching liquids a pH value within this range provides the most satisfactory stabilization, and in most instances a pH of approximately 4.0 is the preferred p-I-I. However, our process is operative anywhere on the acid side, especially within the pH limits of 2.5 to 6.0, and passage of the solution thru adsorbent cellulosic materials results in the removal of impurities and substantial enhancement of the stability of bleaching solutions at any pI-I within these limits. V Cellulosic materials in any form have been found satisfactory for use as the adsorbing agent of our process. Artificial silks generally, as regenerated cellulose, viscose, etc., have been found entirely suitable. We may also use cellulosic materials which have been changed somewhat during the process of their manufacture, such as cellulose acetate. Generally, artificial or regenerated silks prepared from cellulose have been found entirely suitable.

However, as our preferred material, we have found that unchanged cellulosic material, such as that sold commercially under the trade name Kimpak, is an exceedingly efficient adsorbing agent, and one which is very uniform in its action. This material is substantially pure cellulose fibers matted together in the form of a plurality of thin porous sheets. However, it is not essential that pure cellulose be used, for, as previously stated, regenerated cellulose is satisfactory, and we have mentioned pure cellulose only as the particular type of material that we have found to give entirely satisfactory and uniform results. Mixtures of cellulosic materials may also be employed. Thus, a mixture of cellulose acetate and pure cellulose may be used, or a mixture of any cellulose acetate material with other substances which may be more or less inert and which serve as carriers or supporting agents have been found satisfactory.

As an additional step, we have found that the stability of acid bleaching baths, as used in wool bleaching, may also be considerably increased if, in addition to the treatment with a cellulosic adsorbing agent, a stabilizer is added to the bath.

,As such stabilizers we have found p-aminobenzoic acid and acetanilide to be especially suitable. Amounts of either of these stabilizing compounds, ranging from 0.1 gram to 0.3 gram per liter of solution. (0.01% to 0.03% in concentration) will have a beneficial effect in increasing the stability of the bleaching solutions. While the addition of p-aminobenzoic acid, acetanilide, or both, to the bleaching solution will be found effective, it is not essential that these solutions be treated in this way, as merely treatment with the cellulosic adsorbent will be found to increase the stability to such a degree as to render the dilute hydrogen peroxide solution entirely suitable for commercial use in bleach baths. In other words, we wish to emphasize that the addition of the stabilizers is to be utilized as an additional or alternative step and not as an essential element of our process.

As examples of our process for the stabilization of active oxygen yielding bleach baths, the following may be given:

Example 1 An acid solution of hydrogen peroxide of a volume concentration equivalent to approximately 2.0 was passed thru a Kimpak cellulosic adsorbent filter. The pH value of the solution was approximately 3.5. As a comparison, a second sample of the same solution was secured and this solution was not treated by filtration thru the Kimpak.

The volume loss per month of each solution was then determined by means of a 16 hour test for decomposition with each solution. During the test the concentration of the solution was maintained at approximately 2 volumes by the addition of vol. hydrogen peroxide. The volume loss per month of the solution which had been treated by passage thru the cellulosic adsorbent was 4.2, as compared with 10.6 for the solution which had not been so treated, thus showing the superior stabilizing effects obtained by the step of treating the solution with an adsorbent.

Example 2 Two solutions of hydrogen peroxide of volume concentration equivalent to approximately 2.0, and having a pH of 5.0, were secured. One of these solutions was treated by passage thru a Kimpak cellulosic adsorbent (substantially pure cellulose) and then its volume loss per month was determined by means of a sixteen hour test. The second solution, which had not been treated with the cellulosic adsorbent, was also observed to determine its volume loss per month. The untreated solution decomposed at the rate of 22.1 volumes per month, while that which had been filtered thru the adsorbent showed only a volume loss of 3.8 volumes per month. Both solutions during the sixteen hour test periods were of course maintained at approximately 2.0 volume concentration by the addition of 100 volume hydrogen peroxide.

Example 3 stabilizer, was divided into two portions, one of which was treated by passage thru cellulosic adsorbent Kimpak, while the other was not so treated. The Volume losses per month for each solution were determined by means of a sixteen hour test for decomposition, the volume of the solutions being maintained at approximately 2.0 by the addition of more hydrogen peroxide during this test. The values given in the following table clearly show the superior stability of solutions stabilized with acetanilide and treated by filtration thru a cellulosic adsorbent.

Table A Volume losses per month Amount based on 16 hour test g ace Sample Appearance of 4 No. hde pH solution Solutlon Solution added passed H t d svitl i d u i H liter gfigfi Sorbent 0.03 3. 5 Colorless, clear" 2. 0 2. 5 0.03 5.0 ....do.. 1.7 15.7 0.10 3.5 do 1.7 3.0 0.10 5.0 do. 1.3 8.5 0.30 3.5 .do.- 0.8 2.1 0.30 5.0 do 0.0 4.8

Example 4 Further quantities of the two solutions mentioned in Example 3, having a volume concentration of approximately 2.0 and pH values respectively of 3.5 and 5.0, were secured. To these samples p-aminobenzoic acid was added in varying amounts, as specified in the following table. The solutions were then tested as specified in Example 3 for determination of the volume losses per month, based on a sixteen hour test. Each particular solution, containing a specified quantity of the p-aminobenzoic acid, was tested without filtration thru cellulosic adsorbent, and after filtration thru Kimpak. The tests clearly showed the superiority of the process of stabilization by treating the solution with an adsorbing agent, even under those circumstances where the solution contains stabilizers such as p-aminobenzoio acid. It also reveals the superiority of the stabilizing action obtainable by the addition of the stabilizer.

Table B Volume losses per month Amofunt based on 16 hour test 0 Sample p-a1nino- H Appearance of N o. benzoic p solution Solution Solution 7 acid per passed thru not treated liter Kimpek with filter adsorbent 0.03 3. 5 Clear, colorl s 0. 4 1. 2 0.03 5.0 do 0.8 8.9 0. l0 3. 5 Amber.. 0. 0 2. 5 0.10 5.0 do 0.0 7.6 0. 30 3.5 Deep brown 0. 0 1. ,7 0. 30 5.0 .do 0.0 4.4

Wherever in the appended claims reference is made to a solution of hydrogen peroxide, we mean to include within the scope of those claims any material which is equivalent to hydrogen peroxide when in solution. Thus, various peroxides, such as sodium peroxide, magnesium peroxide, etc., might be equivalent under such circumstances, and in acid solution would clearly be equivalent to an acid solution of hydrogen peroxide. It is also conceivable that other per compounds, such as percarbonates, perborates, etc., might be prepared in such a way that the solution obtained would be substantially the equivalent of dilute hydrogen peroxide, acid in reaction.

Wherever in the appended claims reference is made to celluloslc adsorbent, cellulosic adsorbing agent, etc., we mean to include within the scope of that term any form of cellulosic material which will adsorb those catalytic impurities which we have found to be the primary cause of rapid decomposition of acid bleaching solutions of dilute hydrogen peroxide. Thus, any form of cellulose possessing adsorbing characteristics is suitable, as previously indicated, and we mean to include within the scope of our claims all such materials.

We claim:

1. A process for stabilizing a wool bleaching bath consisting essentially of a dilute solution of hydrogen peroxide which is acid in reaction and which contains metallic catalytic impurities serving to promote decomposition which comprises removal of the catalytic impurities by intimately contacting said bleaching bath with an adsorbent material consisting of substantially pure cellulose fibers matted together in the form of a plurality of thin porous sheets, whereby the metallic catalytic impurities are adsorbed.

2. A process for stabilizing a wool bleaching bath consisting essentially of hydrogen peroxide which is acid in reaction and which contains metallic catalytic impurities serving to promote decomposition which comprises the steps of maintaining said bleaching bath at a pH value within the range 2.5 to 6.0 and intimately contacting said bath with an adsorbent material consisting of substantially pure cellulose fibers matted together in the form of a plurality of thin porous sheets, whereby the metallic catalytic impurities are adsorbed and removed.

3. A process for stabilizing a wool bleaching bath consisting essentially of hydrogen peroxide which is acid in reaction and which contains metallic catalytic impurities serving to promote decomposition which comprises the steps of maintaining said bleaching bath at a pH value within the range 2.5 to 6.0, adding a stabilizer selected from the group which consists of para-aminobenzoic acid and acetanilide, and then intimately contacting the bath with an adsorbent material consisting of substantially pure cellulose fibers matted together in the form of a plurality of thin porous sheets, whereby the metallic catalytic impurities are adsorbed and removed. 

